High-speed oscilloscope



Dec. 26, 1950 J. R. PIERCE HIGH-SPEED OSCILLOSCOPE Filed Jan. 26. 1949INVENTOR J. R. PIERCE ATTORNE Patented Dec. 26, 1950 HIGH-SPEEDOSCILLOSCOPE John a. Pierce, Millburn, N. J., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication January 26, 1949, Serial No. 72,799

11 Claims. (01. 250-156) This invention relates to oscilloscopesparticularly such as may be used for observing very high frequencyperiodic signals.

The general objective of the invention is to provide a device forviewing periodic signals and which will respond to frequencies from to500 megacycles or higher.

Another objective is to provide such a device having good voltagesensitivity so as to be adapted to use without an amplifier.

Another objective is to provide such a device presenting a matchedresistive load at the vertical deflecting plate leads.

The usefulness of high speed oscilloscopes for some purposes has beenseriously limited due to lack of sensitivity and band-width limitations.Oscilloscopes operable at very high frequencies have required high levelsignals for their operation and the observation of low level signals hasbeen practically prohibited due to the difliculty of providing signalamplification while meeting the frequency and band-width requirements.

The performance of the oscilloscope of this invention wherebylimitations of former such instruments are overcome is achieved largelythrough two means; the use of optical magnification of the trace on thescreen and the use of a traveling wave deflection system in order toprovide good vertical deflection sensitivity without band-widthlimitation because of transit time.

The invention is explained more fully-in the following description andthe accompanying drawings, in which:

Fig. 1 is a drawing, partly schematic, showing a complete oscilloscopetube and the power supply circuits.

Fig. 2 shows to an enlarged scale certain details of Fig. 1, some ofwhich details are not visible in the Fig. 1 showing.

Fig. 3 shows an alternative to Fig. 2 which may be substituted in theFig. 1 device in place of the parts shown in Fig. 2.

Referring now to the drawings in more detail, Fig. 1 shows a view of theoscilloscope tube from what would normally be the top so that verticaldeflections would be deflections toward and away from the observer ofthe drawing. The evacuated envelope of the tube which may be of glass isdesignated 3. This envelope is provided with an optically ground window33 through which the fluorescent screen 32 may be observed. Thethermionic cathode 31 is coated with electron emissive material on thesurface facing the screen 32. The cathode is connected to lead 39 whichextends through a seal in the envelope. The cathode 31 is heated bymeans of a coil heater 38 in combination with a heat shield 8. Theheater leads are attached to leads 39 and 5 which pass through seals inthe envelope and connect to battery 67 from which energy for the heateris obtained. The cathode 31 is supported by ceramic 9 and a metallicmember I in juxtaposition to a focusing modulator electrode I3.Electrode I0 is spaced from member 1 by ceramic 8 and is spaced by meansof ceramic H from an accelerating electrode I2 which is held positivewith respect to the cathode by means of battery 63 to which it isconnected through lead 35. The cathode 31, electrode [0 and electrode l2cooperate to produce and focus a beam of electrons sharply on a smallaperture [4 centrally located in a metallic disc I 3. The intensity ofthis beam may be controlled by means of a modulating voltage supplied bybattery 68 between cathode 31 and electrode l0, electrode lfl beingconnected to lead 66. The beam emerges from aperture I 4 as a narrowcone of electron flow and passes through the supporting member I5 tofall upon the electron lens formed by electrodes l6, l8 and I 9 whichare supported and insulated from each other by ceramics I1. It will benoted that the assembly of tube elements including member i5 issupported at one end by member 4 fastened to ring 2 which is clamped byscrew 49 around the 'reentrant portion l of the envelope and is held inposition at the other end by members 26 fastened by screws 25 to member28. Electrodes l6 and [9 of the electron lens are at the same potentialas the accelerating electrode l2 and electrode 18 is held at some lowerpotential by means of the tap on battery 63 which is connected to lead65. The potential of electrode I8 is so adjusted as to focus theelectron beam into a small spot, an image of aperture M, on thefluorescent screen 32. The fluorescent material of screen 32 may bedepositedon the side facing the lens and the cathode of a thin sheet ofglass or other transparent material. The fluorescent screen 32 issupported by member 28 which is attached to members 57 and 2|. Anaperture 20 defines and limits the diameter of the electron beam beforeit passes into the region of deflection. The electron beam may bedeflected in a horizontal direction by a voltage source 69 which isapplied through lead 6| to a horizontal deflecting plate 29. Plate 29 issupported from the metallic disc 56 by means of ceramic washers 30 and34 and screw 3|. The disc 56 having an aperture 62 for passage of theelectron beam is held in contact with members 51 and 2|. The otherhorizontal deflecting plate 21 is at the potential of the acceleratingelectrode [2 it being fastened by angle member 23 and screw 24 to disc56 which is connected through members 51 and i5, electrode l2 and lead lto battery 63 as well as to source 39. Vertical deflection isaccomplished by the structure-of Fig. shown in detail in Fig. 2. Thisstructure consists of member 5? and a number of elements mounted thereonmost of which are obscured Fig. 1 by member 2! which is fastened tomember 51 by screws 22 and with member '5! surrounds and shields thedeflecting and other elements mounted on the surface 60 or member 51. InFig. 2, 48, 5| and 58 are three defiectngpl-ates. These areinterconnected by inductances 53 in such a manner as to form a wavefilter. 55 is a combination resistance and inductance which terminatesthe filter formed by plates 48, 5! and 58 and inductances 53 initscharacteristic impedance over a Wide range of frequencies. Theresistance combination 55 is connected at one end to member '5? by thesupporting connector 54 and the associated screw 49. The smooth face Bllof member 5i forms the other plate or side of the vertical deflectingsystem. The deflecting plates 48, 5! and 58 are supported and insulatedfrom member 5'! by the ceramic strips and Washers 45, 59 and -46 andscrews '49. The input 1 end of the filter is connected through aninductance ll, a strip conductor 44 and a lead 59 supported by a ceramicring '43 to the inner conductor '33 of a coaxial transmissionline formedby conductor :36 and outer conductor 35 and shown in Fig. 1. Thistransmission line is designed to have the same characteristic impedanceas the wave filter structure. The coaxial transmission line is sealedthrough the envelope 3 in a vacuum-tight manner as indicated in 1 and avacuum-tight seal AI is made external to the envelope between the innerconductor 36 and outer conductor 35, so that the external connections orvertical deflection terminals :are "at the ends of conductors 35 and 35at A in Fig. l and the pulse or other voltage to be observed may beapplied at this point. The trace on the fluorescent screen 32 may beviewed through the window 33 by means of a microscope.

Fig. 3 shows a deflecting structure which may be used in place of thestructure shown in Fig. 2. It will be seen that the Fig. 3 showing isinterchangeable with the showing of Fig. 2 "and may be substituted forit in Fig. 1. In the Fig. 3 structure the vertical deflecting elementsare the plane.

face -60 of member '5! and an opposing face of a coil 82 which is woundon a ceramic or other insulating core 80 and is proportioned to have thesame characteristic impedance as the terminal ing resistance 83 and thecoaxial line .formed of center conductor 36 and outer conductor 35 of.Fig. 1. The core 80 is supported parallel to face 60 by means of spacers81 and screws 84. One end of resistance 83 is connected to member 51through one of the supporting screws 84.

As transmission lines for the electric wave connected to the terminals35 and 35 at A in Fig. 1 to produce vertical deflections of the electronbeam both the filter structure of Fig. 2 and the coil 92 of Fig. 3 aredesigned so that the phase velocity of the wave traveling along the.filter structure or along the coil is substantially equal to thevelocity of the electron beam. This isv important in order that theadvantages of the deflectinsstructures be realized. Under this conditionthe electron beam which travels along either of the structures betweenit and the face 63 of member 51, in the field of the traveling wave, iscumulatively deflected. The oscilloscope is usable over a wide range offrequencies. It is especially adapted to operate at very highfrequencies and the transmission line deflecting system is more thanone, or several, wavelengths long at'the higher frequencies inorder toprovide high deflection sensitivity. When the device is used at lowfrequencies it is obvious that the line will be shorter as measured inwavelengths and maybe less than one wavelength long.

I-n-a typical case the electron accelerating voltage may be 1000 voltscorresponding to an electron velocity about 6 the speed of light. Themodulator electrode Ill voltage may be zero With respect to the cathodeand the voltage of lens electrode 18 may be about 500 volts with respectto the cathode. The aperture in electrode H1 may be about 0.03 inch indiameter, the aperture l4 may be about 0:001 inch in diameter, theaperture may be about 0.03 inch in diameter and aperture 62 may be about0.040 inch in diameter. The deflecting plates 43., 51 and 53 may bespaced about 0504i inch from the plane face 66 of member 5'! and eachmay be about :inch :long and the deflecting plates 2.? and .29 may beabout inch square and spaced about 0.4 inch apart. The distance fromaperture "F4 to electrode .18 may be 3 inches and the distance fromelectrode I8 to the fluorescent screen 32 may be 3 inches. Theimpedances of the coaxial line formed by and 36 and of the filterlforme'd by 43, 5|, 58 and 53 may be 75 ohms and resistance may be '75ohms. The phase velocity of the filter may be or the speed of light,corresponding to the electron velocity.

It is to be understood that the above-described embodiments areillustrative of the application of the principles of the invention andthe dimensions given are merely typ'i'cal. Other arrangemen'ts may bedevised by those skilled in the art without departing from the spiritand scope of the invention.

What is claimed is:

1. 'An' oscilloscope comprising an evacuated envelope containing acathode, means for pro-- (hiding a beam of electrons along a path fromthe cathode, electron beam deflecting means located along said electronpath remote from the cathode, said deflecting means comprising a highfrequency transmission circuit extending adjacent to said electron pathfor several wavelengths at the highest frequencies used and having awave propagation velocity substantially equal to the velocity of theelectrons in said beam, wherebv the electric field of said circuit isimpressed upon said adjacent electron path and said beam is cumulativelydeflected therealong when the circuit is energized, means for energizingsaid circuit at the end nearer the cathode and a viewing screen locatedin the path of the electron beam beyond said deflecting means.

2. .An oscilloscope comprising an evacuated envelope, means forproducing a beam of electrons along a path within said envelope,electron beam deflecting means located along said path and comprising ahigh frequency transmission circuit extending along said path and havinga wave propagation velocity approximating the velocity of the electronsin :said beam and a viewing screen located in said path beyond :saiddeflecting means.

.3. An oscilloscope comprising am evacuated envelope, means forproducing a beam of electrons along a path within said envelope, meanslocated along said path and excited by the signal to be viewed forproducing a beam deflecting field traveling along a portion of said pathat a velocity approximating the velocity of the electrons in said beamand a viewing screen located in said path beyond the region of saiddeflecting field.

4. In combination, means for producing a beam of electrons along a pathwithin an evacuated envelope, electron beam deflecting means locatedalong said path, said deflecting means comprising a high frequencynon-resonant transmission circuit extending along said path and having awave propagation velocity approximating the velocity of the electrons insaid beam and a viewing screen located in said path beyond saiddefleeting means.

5. In combination, means for producing a beam of electrons along a pathin an evacuated envelope, means located along said path and excited by asignal to be viewed for producing an electron beam deflecting fieldtraveling along a portion of said path at a velocity approximating thevelocity of the electrons in said beam, and a viewing screen located insaid path beyond the region of said deflecting field. I

6. An oscilloscope comprising an evacuated envelope containing acathode, electrodes for producing an electron beam along a path fromsaid cathode to a viewing screen, electron beam deflecting means locatedalong said path and adjacent thereto comprising a high frequencytransmission circuit producing when energized altravelin electric fieldin a portion of said path traveling in the same direction as saidelectron beam and at substantially the same velocity as said electronbeam, said transmission circuit being positioned to deflect the electronbeam in a certain plane, and another deflecting means producing whenenergized an electric field in a portion of said path and positioned todeflect the electron beam in a plane at an angle to" said certain plane.

7. An oscilloscope comprising an evacuated envelope within which are twoelectron beam deflecting systems each arranged to produce an electricfield for deflecting an electron beam in one of two planes which aresubstantially perpendicular to each other, one of said deflectingsystems comprising an electric wave transmission circuit extending alongthe path of said electron beam and arranged to produce one of saidelectric fields traveling along said circuit at a velocity within therange of practical electron velocities and means within said envelopefor projecting said beam of electrons at a velocity substantially thesame as the velocity of said traveling field through both said fields toa viewing screen, the electron beam passing through said traveling fieldin the direction of travel of the field.

8. An oscilloscope comprising an evacuated envelope containing acathode, a viewing screen, means for projecting a beam of electrons fromsaid cathode along a path to said viewing screen and electron beamdeflecting systems for deflecting said beam in two planes angularlydisplaced from each other, one of said deflecting systems 7 comprising afilter type of high frequency transmission circuit extending along saidelectron beam path, said circuit comprising a metallic member presentinga surface to one side of the electron beam path, a plurality of metallicmenibers presenting surfaces opposed to said firstmentioned metallicmember and arranged along said beam path on the side opposite saidfirstmentioned metallic member so that the electron beam passes betweensaid surface of said firstmentioned metallic member and the group ofsaid surfaces of said plurality of metallic members, inductancesinterconnecting the said plurality of metallic members whereby theinterconnecting inductances and the capacitances between saidfirst-mentioned metallic member and said plurality of metallic membersform said filter type high frequency transmission circuit, means forapplying high frequency deflecting voltage to said transmission circuitbetween one of said plurality of metallic members and saidfirst-mentioned metallic member and a terminating load for said circuitconnected between another one of said plurality of metallic members andsaid first-mentioned metallic member.

9. An oscilloscope comprising an evacuated envelope containing acathode, a viewing screen, means for projecting a beam of electrons fromsaid cathode along a path to said viewing screen and electron beamdeflecting systems for deflecting said beam in two planes angularlydisplaced from each other, one of said deflecting systems comprising ahelical coil type of high frequency transmission circuit extending alongsaid electron beam path, said last-mentioned deflecting systemcomprising a metallic member presenting a surface to one side of theelectron beam path, a helical coil axially parallel to said beam pathand positioned therealong presenting a coil surface opposed to saidsurface of said metallic member and on the opposite side of said beampath from the said surface of said metallic member so that the electronbeam passes between said surface of said metallic member and said coilsurface, means for applying high frequency deflecting voltage to saidtransmission circuit between said coil and said metallic member and aterminating load for said circuit connected between said coil and saidmetallic member.

10. An oscilloscope according to claim 9 having a window in saidenvelope for observation of said viewing screen.

11. An oscilloscope comprising an evacuated envelope containing acathode, a viewing screen, means for projecting a beam of electrons fromsaid cathode along a path to said viewing screen, electron beamdeflecting systems for deflecting said beam in two planes angularlydisplaced from each other, one of said deflecting systems comprising ahigh frequency transmission circuit extending along said path andcapable of producing a traveling electric field along a portion of saidpath and traveling in the same direction as the electron beam and atsubstantially the same velocity as said beam and means for energizingsaid circuit with a deflecting voltage.

JOHN R. PIERCE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,932,084 Opsahl Oct. 24, 19332,263,733 Knoll Nov. 25, 1941 2,425,682 Liebmann Aug. 12, 1947 2,463,617Hartley Mar. 8, 1949

